It is desirable to devise a permanent magnet excited mechanism for transmitting variable torque in drive applications. Specifically there is a need to couple constant speed devices such as motors or engines to variable output speed and torque devices such as pump impellers, fans, propellers, wheels, etc. Transmission devices including various eddy current clutches have been in use for some time in various forms. An examination of the prior art shows that these eddy current devices are limited to three general types    1. Fixed gap clutches that use permanent magnets. These devices are limited to specific set gaps and output torque and are specific to low torque applications.    2. Eddy current clutches that use DC current to generate and vary the flux density in a fixed gap mechanism. These devices are available in a wide range of horse power but are expensive, complicated and require a DC current and control to induce the torque. There are applications where the DC current is not desirable or where the apparatus for controlling the torque producing currents are unreliable.    3. Current variable gap permanent magnet disk clutches are limited in their ability to transmit large amounts of torque and are constructed in a manner which causes instability at higher speeds. These limitations relegate the practical application of these devices to low speed, low horsepower application.
The apparatus described utilizes recent developments in magnetic material technology, in conjunction with architecture designed for mechanically stable operation. This will allow the apparatus to be used in a full range of power transmission applications including high horsepower applications. The configuration of the device also makes it stable and able to operate at higher input speeds, which are natively present in some motors and engines.
The described apparatus is a device that uses permanent magnets and conductors arranged in an optimal manner to generate the magnetic flux in a power transmission drive. The embodiments described utilize a mechanical means for changing the flux density between two rotating components to vary the torque transmitted by and thereby the output speed of the apparatus.